1. Field of the Invention
The present general inventive concept relates to a digital-to-analog converter (DAC), and more particularly, to a DAC of a source driver circuit to drive a liquid crystal display (LCD) apparatus.
2. Description of the Related Art
A digital-to-analog converter (DAC) is a core block of a source driver circuit that drives a liquid crystal display (LCD) device.
In general, a source driver circuit mainly uses a resistor-based DAC (hereinafter referred to as “R-DAC”).
FIG. 1 is a circuit diagram illustrating a conventional R-DAC 100.
Referring to FIG. 1, the conventional DAC 100 includes a string of resistors 110, a decoder 120, and an amplifier (OP-AMP) 130. In order to generate a plurality of voltages, the string of the resistors 110 include a plurality of resistors 1st R through 2nth R that are connected in series between a first node for receiving a first reference voltage Vref1 and a second node for receiving a second reference voltage Vref2 (Vref2<Vref1). The decoder 120 selects one of the voltages and outputs it as a selected voltage DECO, in response to an input digital signal DATA.
A DAC that converts 8-bit digital data DATA into an analog signal, i.e., an 8-bit DAC, requires 28(=256) resistors and 28 metal lines. Accordingly, the decoder 120 is embodied as a 256:1 decoder capable of selecting a voltage from among 256 voltages.
As a bit value of the digital data DATA increases, a total numbers of resistors and metal lines required exponentially increase. For example, if the digital data DATA is 10 bits long, 1024(=210) resistors, 1024 metal lines, and a 1024:1 decoder are needed.
The string of resistors 110 can be shared for all channels, but the decoder 120 and the amplifier 130 are prepared in channel units. Accordingly, a size (or area) of the DAC 100 is slightly influenced by an increase in the total number of the string of the resistors 110 but is significantly influenced by the size of the decoder 120. For example, a size of the 1024:1 decoder must be four times greater than a size of a 256:1 decoder, thus making it very difficult to manufacture a source driver. Also, a total number of metal lines via which a plurality of voltages that are divided by the string of the resistors 110 are transmitted to respective channels, is significantly increased, for example, from 256 to 1024, thereby also limiting to manufacturing of a source driver.
Therefore, there is a need for development of a method of reducing a total number of resistors and metal lines, and a size of a decoder in order to reduce a size of a DAC.